Since a carbon fiber reinforced plastic is lightweight and high-strength, it is used in various fields such as a member of airplane or automobile, a concrete reinforcing material, a sporting gear etc. In particular, since a demand for a weight saving of a member of airplane or automobile has recently been growing because of concerns about energy issues, a ratio of using a carbon fiber reinforced plastic is increasing.
As a method for producing these carbon fiber reinforced plastics, mention may be made of an autoclave molding of laminating a sheet which an epoxy resin is preliminarily impregnated and thereby bagging them and molding them at autoclave by applying temperature and pressure, a compression molding using a prepreg sheet, and a filament winding (FW) molding of impregnating and rewinding a temperature controlled resin. The autoclave molding makes it possible to give a pressure uniformly to obtain parts having a complicated shape. However, since there are some problems that it needs a long cure time, and the use of the autoclave or a special kind of subsidiary material, an improvement is required. Since the compression molding requires a mold, it is difficult to apply many kinds of small quantities production, and a shape produced by FW molding is limited. In order to solve these problems, a RTM (Resin Transfer Molding) or VaRTM (Vacuum assisted Resin Transfer Molding) methods wherein a dry preform of carbon fibers is set into a mold to inject an epoxy resin to heat and cure, are recently developed. However, there are still problems that a heating of resin during injection is required, or a cure time is long, or a cure at a high temperature is required, or a lifetime of a mold is short or a residual void exists. Moreover, in the case that unsaturated polyester resin wherein it has a good performance in a glass fiber reinforced plastics, a molding time is short, and a workability and a hardenability is superior, is applied as a matrix of a carbon fiber reinforced plastic, although a formability is good, but in the present circumstances it is impossible to obtain sufficient mechanical properties.
It is known that urethane (meth) acrylate has superior adhesion properties to carbon fibers historically, it is used as a sizing agent of carbon fibers (For example, Patent literature 1).
Moreover, it is suggested that since urethane (meth) acrylate has a good adhesion properties to a reinforced fiber, it can be used by mixing it with a resin having inferior adhesion properties to a reinforced fiber (For example, Patent Literature 2).